In metallurgical processes, waste gases from electric furnaces or similar reactors frequently contain molten particles and/or vaporous constituents which upon cooling and/or oxidation tend to form very fine solid particles which can clog the waste gas conduit by formation of crusts. Such problems resulting from the clogging of the waste gas conduit are known for instance from slag cleaning furnaces in the copper industry, electric furnaces in the secondary metallurgic industry (copper, lead), or plasma furnaces in the production of titanium dioxide slag (TiO2 slag).
To prevent this formation of crusts, it has been proposed to add air to the waste gas stream in the waste gas conduit in a controlled or uncontrolled manner. For example, EP 0 661 507 A1 describes a process wherein a cooled partial stream of a clean gas is admixed to the waste gas stream before its entry into a gas cleaning plant. According to EP 0 661 507 A1, dust particles can additionally be introduced into the waste gas, which serve as condensation nuclei. By condensation of volatile metal compounds on the dust particles, while at the same time cooling the waste gas below a temperature which can lead to the particles being sintered on the inner wall surfaces of the gas conduits, the deposit of condensates on these inner wall surfaces should be avoided. In practice, however, this process has not led to satisfactory results, so that the deposits in the waste gas conduits still have to be removed “by mining” in regular intervals.